This invention relates to the conversion of paraffins into more valuable olefinic and aromatic products. In particular, the invention relates to controlling the fluidization regime of a fluidized bed of catalyst to improve selectivity toward valuable olefinic and aromatic products and away from methane and ethane.
Conversion of paraffinic feedstocks to more valuable aromatic and olefinic product streams is known. For example, U.S. Pat. No. 3,756,942 discloses a process for the preparation of aromatic compounds in high yields which involves contacting a particular feed consisting essentially of mixtures of paraffins and/or olefins, and/or naphthenes with a crystalline aluminosilicate, e.g. ZSM-5, under conditions of temperature and space velocity such that a significant portion of the feed is converted directly into aromatic compounds. U.S. Pat. No. 3,759,821 discloses a similar process for upgrading catalytically cracked gasoline. Finally, U.S. Pat. No. 3,760,024 teaches a process for the preparation of aromatic compounds which involves contacting a feed consisting essentially of C.sub.2 -C.sub.4 paraffins and/or olefins with a crystalline aluminosilicate, e.g. ZSM-5. The above references are incorporated herein by reference and are cited in particular for descriptions of useful feedstocks and process conditions.
Conversion has been found to be enhanced in fluidized bed processes by maintaining the fluidized bed reaction zone in a turbulent regime. For example, U.S. Pat. No. 4,547,616 to Avidan et al. teaches a process for the conversion of oxygenates to lower olefins in a turbulent fluidized bed of catalyst. U.S. Pat. No. 4,746,762 to Avidan et al. teaches a process for upgrading light olefins in a turbulent fluidized catalyst bed reactor. The Avidan et al. references are incorporated herein by reference and are cited in particular for the details of fluidized-bed operating variables. While conversion improvements using turbulent fluidized beds have been reported, previous processes have failed to address controlling the fluidization regime to affect a shift in selectivity toward more desirable products.
In particular, the paraffin upgrading processes described by the references cited above produce product streams which comprise aliphatic and aromatic compounds together with hydrogen. The most economically attractive of these compounds are light olefins such as ethylene and propylene, C.sub.5 + gasoline rich in aromatics, and hydrogen while the least desirable are methane and ethane. Further, hydrogen evolved in such upgrading processes may be consumed elsewhere in a refinery or petrochemical plant in processes such as lubricant dewaxing, catalytic desulfurization and catalytic reforming. Relatively unreactive and difficult to upgrade into more valuable products, methane and ethane are typically flared or burned as fuel gas. Thus, it can well be seen that it would be highly desirable to shift the yield of a paraffin upgrading process away from methane and ethane and toward hydrogen, light olefins such as ethylene and propylene and C.sub.5 + gasoline rich in aromatics.